Field of the Invention
The present invention relates to a power management integrated circuit (IC), and more particularly, to a gamma voltage supply circuit and method which is capable of stably supplying a gamma voltage in response to the change of external voltage, and a power management IC having the same.
Description of the Related Art
A display system includes a flat panel employing a display panel such as a liquid crystal display and a power management IC to supply power to internal parts thereof.
The power management IC may be implemented in the form of a chip, and configured to generate voltages required for operations of a source driver IC, a gate driver IC, a timing controller, and the display panel. In particular, the power management IC includes a gamma voltage supply circuit therein, and supplies a gamma voltage generated by the gamma voltage supply circuit to the source driver IC. The gamma voltage is used in the source driver IC so as to express an image using data.
Furthermore, the power management IC is configured to generate a variety of voltages, such as a source driving voltage for the source driver IC, gate high and low voltages for the gate driver IC, and a common voltage required for driving the liquid crystal display, as well as the gamma voltage. Furthermore, the power management IC commonly uses an external voltage to generate the above-described voltages. That is, the gamma voltage supply circuit commonly uses an external voltage to generate the gamma voltage.
In a power environment where the above-described external voltage is commonly used, a load may be suddenly changed. In this case, the gamma voltage may be destabilized by the influence of the sudden change of load.
For example, the source driver IC performs an operation of temporarily consuming a large amount of current so as to drive a large number of pixels corresponding to one line at the same time. That is, a sudden change of load may occur in the source driver IC. Thus, the level of the external voltage may be rapidly changed in response to the sudden change of load.
When the level of the external voltage applied to the power management IC is rapidly changed by the above-described load change, the gamma voltage supply circuit is influenced by the change in level of the external voltage. That is, the gamma voltage generated through the external voltage may significantly drop. Thus, when the gamma voltage is destabilized, an image quality may be degraded.
In order to prevent the gamma voltage from being destabilized, the gamma voltage supply circuit of the power management IC may have a filter mounted therein, the filter including a resistor and a capacitor. However, the filter may relieve the instability of the gamma voltage, but has difficulties in completely overcoming the instability. Furthermore, in order to sufficiently overcome the instability of the gamma voltage, a capacitor having a large capacity may be required. In this case, however, the size of the power management IC, that is, the chip size may be inevitably increased.